Our long term objective is to define and, if possible, alter the mechanisms that modulate cellular damage during tissue hypoxia. Specifically, we propose to study the effect the glucose concentration and intracellular pH have on cellular function during a severe hypoxic insult. the hypotheses to be tested in this proposal are: 1) Total ischemia is less harmful to normal cellular function than partial ischemia or hypoxemia. 2) Cellular damage is directly related to the rate of glycolysis during hypoxia. 3) Decreasing the production of lactate ameliorates hypoxic cellular damage. 4) The effect of glucose on normal cellular function during hypoxia is mediated through decreases in intracellular pH (pHi). These hypotheses will be tested in a perfused rabbit skeletal muscle preparation exposed to different levels of ischemia and hypoxemia. Ischemia is defined as a decrease in perfusate flow, hypoxemia as a lowering of the perfusate oxygen concentration and hypoxia refers to a decrease in tissue PO2. 31-Phosphorus magnetic resonance spectroscopy (31P MRS) will be used to follow sequential changes in pHi and bioenergetic parameters in individual animals. Analytical methods will be used to measure the tissue concentration of high energy phosphates, glycogen, pyruvate, lactate and the products of purine nucleotide degradation and lipid peroxidation. Specially designed surface PO2 and pH microelectrode arrays will measure tissue PO2 and extracellular pH (pHe) during ischemia and hypoxemia. The pHe will be correlated with the pHi obtained with 31P MRS and that calculated from the lactate and pyruvate concentrations. We will attempt to define mechanisms of hypoxic injury by correlating measures of physiological function, morphology, and biochemical markers of cellular dysfunction. The information to be obtained in these experiments may have great importance in understanding the mechanisms leading to cell injury during ischemia and reperfusion, or hypoxemia and reoxygenation. Myocardial infarction and cerebral stroke are examples of the former, while respiratory failure is an example of the latter.